The erosion of dental enamel can lead to pain, discoloration, mechanical failure, and greater susceptibility to dental carries. Chemical erosion of tooth enamel may arise from the presence of acid in the oral cavity. Saliva constituents, mainly proteins and minerals, along with the pellicle are integral in protecting against an erosive challenge. The minerals and proteins in saliva help provide a chemical barrier to slow down or shift the complex dynamic equilibria of hard tissue demineralization, while the pellicle will provide a diffusion barrier to accomplish the same process.
An oral care composition may protect teeth in a variety of ways. Many oral care compositions are designed to increase the pH in the oral cavity. A common strategy when attempting to control oral pH is to include an alkaline agent in the formulation of the oral care composition. The alkaline agent reacts with acid to neutralize the acid, forming water and a salt. This process raises the pH in the oral cavity. However, even when the pH in the oral cavity is high, the pH at the surface of the teeth, where cariogenic bacteria may be present, may be locally lower than the oral cavity in general due to bacterial activity. Soluble bases are not able to preferentially locate at the tooth surface, where acid does the most damage to teeth.
Metal ions are able to protect teeth from erosion. Certain metal ions can react with the surface of the enamel to shift the solubility equilibrium away from dissolution of the tooth's enamel. Some examples of ions that have been investigated for this purpose are calcium, zinc, tin, aluminum, strontium and others. Phosphate salts of these metals have been particularly interesting due to the high phosphate content in dental enamel.
Insoluble or slightly soluble metal compounds have been investigated as metal ion sources for tooth remineralization. By combining insoluble metal compounds with polymers, the insoluble compounds become more easily dispersed in the oral care composition. Additionally, the polymers may improve the residence time of the metal agent in the oral cavity. However, the main benefit of having a source of metal ions would be achieved at the surface of the tooth. Accordingly, there is a need for a long lasting oral care composition that can deliver metal containing compounds to and control pH at the surface of the tooth to prevent dental erosion.